So obviously many of the LPs appear to make these investments not really knowing much detail..

I was recently sent details about a 20-unit apartment complex that I’m interested in, but the seller's asking price doesn’t align with the numbers I’ve run.

I know there's a lot of details missing to actually give an accurate answer.

The guru your son is learning this technique from is likely not telling your son that the deal will almost certainly encourage your son to get an "off-market" deal from a "wholesaler" who is unlikely to properly disclose the details of the property or encourage an inspection. 

I also believe there is a small co-op in La Jolla but only infrequent sales so not good for estimating a discount.

The best advice I can give you for seeking counsel in online forums is learn how to ask specific questions and provide as much detail as you can. 

For instance, mismatched names, employment details, or salary figures should warrant further scrutiny.Urgency to Move In: Applicants who are unusually pushy about quick move-in dates may be attempting to bypass thorough checks.Reluctance to Provide References: Hesitation or refusal to provide contactable references from previous landlords or employers is a cause for concern.Cash Offers for Faster Move-In: Proposals to pay a significant amount up front, especially in cash, to expedite the moving process can sometimes indicate an attempt to avoid scrutiny.Unverifiable Identity: Difficulty in verifying the applicant’s identity through standard identification documents can indicate potential fraud.Tips to Mitigate Rental Application Fraud:Enhance Verification Processes: Implement stringent verification processes for employment, previous rental history, and identity.

You should estimate th property value using recent sales data.

@Mark F Thanks for the detailed response! 

Here's a detailed guide on how to screen applicants: Application Screening Guide